Ink set, recording apparatus, and recording method

ABSTRACT

An ink set includes a cyan ink composition containing C. I. Pigment Blue 15:6 as a pigment; a magenta ink composition containing a quinacridone pigment selected from the group consisting of C. I. Pigment Violet 19, C. I. Pigment Red 122, C. I. Pigment Red 202, and C. I. Pigment Red 209 or a quinacridone solid solution pigment composed of at least two selected from the group; a yellow ink composition containing a pigment selected from the group consisting of C. I. Pigment Yellow 74, C. I. Pigment Yellow 213, and C. I. Pigment Yellow 185; a light magenta ink composition containing a quinacridone pigment selected from the group consisting of C. I. Pigment Violet 19, C. I. Pigment Red 122, C. I. Pigment Red 202, and C. I. Pigment Red 209 or a quinacridone solid solution pigment composed of at least two selected from the group at a pigment concentration lower than that of the magenta ink composition; and a light cyan ink composition containing C. I. Pigment Blue 15:3 as a pigment at a pigment concentration lower than that of the cyan ink composition.

BACKGROUND

1. Technical Field

The present invention relates to an ink set with an extended colorreproduction range (gamut), and particularly to an ink set having anextended color reproduction range in a blue region of a dark portion andexcellent color reproducibility in other color regions. Also, thepresent invention relates to a recording apparatus and recording methodusing the ink set.

2. Related Art

A CIE/L*a*b* color system is known as a color model. According to theCIE/L*a*b*, all colors (spectra) in a visible light region which can beobserved by the human eye can be indicated by chromaticity coordinates.

Among the three parameters (L*, a*, b*) of the CIE/L*a*b* color system,L* represents luminance (brightness) and a* and b* representchromaticity showing hue and saturation. When L*=0, a black color isindicated, and when L*=100, a white color is indicated. In addition, a*represents a position between red and green colors, and negative valueand positive value indicate green and red, respectively. Further, b*represents a position between yellow and blue colors, and negative valueand positive value indicate blue and yellow, respectively. Since theL*a*b* color model is tree-dimensional, a color space is expressed by athree-dimensional space in which luminance is represented on thevertical axis.

However, the L*a*b* color model is merely an index used for conceptuallyexplaining a color space, and the color reproduction range is limited.Namely, for example, when an image is formed on a recording medium usinga pigment-based ink or ink set, a color which cannot be reproduced by acolor of the L*a*b* color model is present.

On the other hand, ink compositions containing various pigments withhigh color development have been proposed. Japanese Unexamined PatentApplication Publication No. 2006-282810 discloses that an ink havinghigh color development and excellent ejection stability, storagestability, and ink reliability for clogging and the like is preparedusing an ink composition containing a quinacridone solid solutionpigment, a polyether-modified polydimethylsiloxane compound, and water.In addition, Japanese Unexamined Patent Application Publication No.2007-186641 discloses that an ink having excellent printability,ejection stability, storage stability, and ink reliability for cloggingand the like is realized using an ink composition containing asurface-treated pigment (yellow, magenta, cyan) including hydrophilicdispersive groups bonded to the surfaces of a solid-solution pigmentcomposed of two or more specified pigments, a water-insoluble vinylpolymer, and water.

However, in particular, in a blue region of a dark portion having a L*value of 20 or less, color reproduction is limited. That is, whenluminance is low, chromaticity and saturation are not easily expressed,and thus, for example, a color with an L* value of 20 or less, an a*value of 30 or more, and a b* value of −75 or less, such as (L*, a*,b*)=(19.4, 30.0, −72.6) or (L*, a*, b*)=(19.4, 37.6, −76.8) in theCIE/L*a*b* color system, cannot be reproduced on an image recordingmedium using droplets (ink). Therefore, the inventors intensivelystudied in order to extend a color reproduction range in a blue regionof a dark portion. As a result, the inventors have proposed in JapanesePatent Application No. 2008-215056 as prior application that the colorreproduction range in a blue region of a dark portion with a L* value of20 or less can be extended by an ink set including a combination of acyan ink composition containing C. I. Pigment Blue 15:6 or C. I. PigmentBlue 60 as a pigment and a magenta ink composition containing aquinacridone pigment. In particular, it has been proposed that a colorwith a L* value of 20 or less, an a* value of 30 or more, and a b valueof −75 or less, which has so far been impossible to reproduce, can berealized by an ink set including a combination of a cyan ink compositioncontaining C. I. Pigment Blue 15:6 as a pigment and a magenta inkcomposition containing a quinacridone solid solution pigment.

On the other hand, with respect to an ink set, generally, a blue regioncolor is reproduced by mixing a cyan ink composition and a magenta inkcomposition, a red region color is reproduced by mixing a yellow inkcomposition and a magenta ink composition, and a green region color isreproduced by mixing a yellow ink composition and a cyan inkcomposition. Therefore, when the color reproduction range in a blueregion is extended, it is necessary to take account of colorreproducibility in a green region which is reproduced by a cyan inkcomposition and a yellow ink composition and in a red region which isreproduced by a yellow ink composition and a magenta ink composition.Namely, it is necessary to simultaneously satisfy the color reproductionranges in the blue region and the other color regions. On the otherhand, the inventors have found that although C. I. Pigment Blue 60contained in a cyan ink composition is an effective pigment type forenlarging the reproduction range in the blue region of a dark portion,the pigment significantly decreases the color development in the greenregion. Therefore, it has been proposed in Japanese Patent ApplicationNo. 2008-232165 that reproducibility in both the blue region and thegreen region can be realized by an ink set including a combination of acyan ink composition containing C. I. Pigment Blue 15:6 as a pigment, amagenta ink composition containing a quinacridone pigment selected fromthe group consisting of C. I. Pigment Violet 19, C. I. Pigment Red 122,C. I. Pigment Red 202, and C. I. Pigment Red 209 or a quinacridone solidsolution pigment composed of at least two selected from the group, and ayellow ink composition containing a pigment selected from the groupconsisting of C. I. Pigment Yellow 74, C. I. Pigment Yellow 213, and C.I. Pigment Yellow 185.

However, the inventors have recently found that C. I. Pigment Blue 15:6contained as a pigment in a cyan ink composition has poor graininess forrecoding an image in a high-brightness region. An ink set is generallycomposed of a cyan ink composition, a magenta ink composition, a yellowink composition, a light cyan ink composition, and a light magenta inkcomposition. In order to improve gradation and graininess, an inkcomposition (light ink composition) at a lower pigment concentrationamong the similar color ink compositions in the ink set is used forrecording an image in a high-brightness region. However, it has beenfound that a problem with graininess, such as noticeable dots or thelike, occurs in a high-brightness cyan region and green region in whichan image is recorded using a light cyan composition containing C. I.Pigment Blue 15:6 as a pigment.

SUMMARY

An advantage of some aspects of the invention is that the inventionprovides an ink set having an enlarged color reproduction range (gamut)and excellent graininess in a high-brightness region.

Another advantage of some aspects of the invention is that the inventionprovides a recording method and a recording apparatus using the ink set.

The present invention has been achieved on the basis of theabove-described findings and is as follows.

(1) An ink set including:

a cyan ink composition containing C. I. Pigment Blue 15:6 as a pigment;

a magenta ink composition containing a quinacridone pigment selectedfrom the group consisting of C. I. Pigment Violet 19, C. I. Pigment Red122, C. I. Pigment Red 202, and C. I. Pigment Red 209 or a quinacridonesolid solution pigment composed of at least two selected from the group;

a yellow ink composition containing a pigment selected from the groupconsisting of C. I. Pigment Yellow 74, C. I. Pigment Yellow 213, and C.I. Pigment Yellow 185;

a light magenta ink composition containing a quinacridone pigmentselected from the group consisting of C. I. Pigment Violet 19, C. I.Pigment Red 122, C. I. Pigment Red 202, and C. I. Pigment Red 209 or aquinacridone solid solution pigment composed of at least two selectedfrom the group at a pigment concentration lower than that of the magentaink composition; and

a light cyan ink composition containing C. I. Pigment Blue 15:3 as apigment at a pigment concentration lower than that of the cyan inkcomposition.

(2) The ink set described above in (1), wherein the pigment contained inat least one of the magenta ink composition and the light magenta inkcomposition is a quinacridone solid solution pigment composed of atleast two selected from the group consisting of C. I. Pigment Violet 19,C. I. Pigment Red 122, C. I. Pigment Red 202, and C. I. Pigment Red 209.

(3) The ink set described above in (2), wherein the pigment contained inat least any one of the magenta ink composition and the light magentaink composition is a quinacridone solid solution pigment composed of C.I. Pigment Violet 19 and C. I. Pigment Red 202.

(4) The ink set described above in (3), wherein in the quinacridonesolid solution pigment, the mass of C. I. Pigment Violet 19 is largerthan the mass of C. I. Pigment Red 202.

(5) The ink set described above in (3) or (4), wherein in thequinacridone solid solution pigment, the mass ratio of C. I. PigmentViolet 19/C. I. Pigment Red 202 is 70/30 to 50/50.

(6) The ink set described above in any one of the terms (1) to (5),wherein C. I. Pigment Violet 19 contained in the quinacridone solidsolution pigment is γ-type.

(7) The ink set described above in any one of the terms (1) to (6),wherein the pigment concentration of each of the light magenta inkcomposition and the light cyan ink composition is 2% by mass or less.

(8) The ink set described above in any one of the terms (1) to (7),including the cyan ink composition, the magenta ink composition, theyellow ink composition, the light magenta ink composition, the lightcyan ink composition, and a black ink composition.

(9) A recording apparatus including the ink set described above in anyone of the terms (1) to (8).

(10) A recording method using the ink set described above in any one ofthe terms (1) to (8).

A ink set according to the present invention includes a light cyan inkcomposition used for recording images in a high-brightness region, thepigment type used in the light cyan ink composition being different fromthat in a cyan ink composition of a higher concentration than the lightcyan ink composition. Namely, the light cyan ink composition uses C. I.Pigment Blue 15:3 of a pigment type different from C. I. Pigment Blue15:6 which is a pigment type of the cyan ink composition. Theconfiguration permits the formation of a high-quality image withexcellent graininess in a high-brightness cyan region and green regionwhere an image is recorded with a light cyan ink composition.

Therefore, the ink set according to the present invention can reproducea color in a dark portion blue region having an L* value of 20 or less,an a* value of 30 or more, and a b* value of −75 or less according toCIE standards, which has so far been impossible to reproduce. Also, theink set has excellent color reproducibility in a green region and canform a high-quality image with excellent graininess even in ahigh-brightness cyan region and green region.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a drawing showing gamuts at L*=20 of ink sets of Example 1 andComparative Examples 1 and 2.

FIG. 2 is a drawing showing gamuts at L*=20 of ink sets of Example 2 andComparative Examples 3 and 4.

FIG. 3 is a drawing showing gamuts at L*=10 to 90 of, ink sets ofComparative Examples 3 and 4.

FIG. 4 is a drawing showing gamuts at L*=10 to 90 of ink sets of Example2 and Comparative Example 3.

FIG. 5 is a drawing showing gamuts at L*=10 to 90 of ink sets of Example2 and Comparative Example 4.

FIG. 6 is a chart showing graininess in green regions of ink sets ofExample 3 and Comparative Example 5.

FIG. 7 is a chart showing graininess in cyan regions of ink sets ofExample 3 and Comparative Example 5.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A cyan ink composition, a magenta ink composition, a yellow inkcomposition, a light cyan ink composition, and a light magenta inkcomposition which constitute an ink set according to the presentinvention are described in detail below.

1. Pigment

In the present invention, commercially available C. I. Pigment Blue 15:6(hereinafter, abbreviated as “P. B. 15:6”) can be used in a cyan inkcomposition.

Also, commercially available C. I. Pigment Violet 19 (hereinafter,abbreviated as “P. V. 19”), C. I. Pigment Red 122 (hereinafter,abbreviated as “P. R. 122”), C. I. Pigment Red 202 (hereinafter,abbreviated as “P. R. 202”), and C. I. Pigment Red 209 (hereinafter,abbreviated as “P. R. 209”) can be used as quinacridone pigments in amagenta ink composition and a light magenta ink composition.

In the present invention, a quinacridone solid solution pigment iscomposed of at least two selected from the group consisting of P. V. 19(in a solid solution, γ-type P. V. 19 is preferred from the viewpoint ofcolor development), P. R. 122, P. R. 202, and P. R. 209.

A combination of two or more quinacridone compounds is not particularlylimited. However, in the present invention, a solid solution pigmentincluding a combination of P. V. 19 and P. R. 209, a combination of P.V. 19 and P. R. 122, or a combination of P. V. 19 and P. R. 202 ispreferred from the viewpoint of color development. In particular, asolid solution pigment including a combination of P. V. 19 and P. R. 202is preferred.

The mixing ratio of P. V. 19 and P. R. 209 in the solid solution pigmentis preferably P. V. 19:P. R. 209 in a range of 10:90 to 90:10, morepreferably in a range of 15:85 to 85:15, and particularly preferably ina range of 30:70 to 50:50. In addition, P. V. 19:P. R. 122 is preferablyin a range of 10:90 to 90:10, more preferably in a range of 15:85 to85:15, and particularly preferably in a range of 30:70 to 50:50.Further, P. V. 19:P. R. 202 is preferably in a range of 10:90 to 90:10,more preferably in a range of 15:85 to 85:15, and particularlypreferably in a range of 30:70 to 50:50. When a quinacridone pigment isformed in the solid solution pigment, it is possible to form a magentaink composition and a light magenta ink composition having excellentcolor reproducibility in a red region with high coloration and highbrightness and excellent color reproducibility in a violet region. Inparticular, a solid solution pigment including P. V. 19 and P. R. 202 inwhich the mass of P. V. 19 is larger than the mass of P. R. 202 isexcellent in color reproducibility in a red region with high colorationand high brightness and excellent in color reproducibility in a violetregion.

The method for producing the quinacridone solid solution pigment is notparticularly limited, and a known production method can be used.Specifically, the methods disclosed in Japanese Unexamined PatentApplication Publication Nos. 11-49998, 2000-319534, and 2003-253150 canbe used. In addition, in the present invention, the quinacridone solidsolution pigment represents a pigment which is present as a mixedcrystal (crystallized in a mixed state) of a plurality of quinacridonepigment molecules and is different from a simple mixture of two or morequinacridone pigments.

In addition, whether or not a solid solution pigment composed of two ormore quinacridone pigments can be easily confirmed by X-ray diffractionanalysis. In case of a simple mixture of two types of quinacridonepigments, an X-ray diffraction pattern thereof corresponds to overlap ofthe X-ray diffraction patterns of respective pigments, and the peakintensity is proportional to the mixing ratio. On the other hand, when aquinacridone solid solution pigment is formed, a diffraction patternpeculiar to a newly formed crystal is observed.

In the present invention, the average particle diameter of thequinacridone solid solution pigment is preferably in a range of 10 nm to200 nm and more preferably in a range of 50 nm to 150 nm. When theaverage particle diameter is less than 10 nm, weather resistance may bedecreased, while when the average particle diameter exceeds 200 nm,precipitation may occur, thereby failing to stably eject the ink.

In addition, commercially available C. I. Pigment Yellow 74(hereinafter, abbreviated as “P. Y. 74”), C. I. Pigment Yellow 213(hereinafter, abbreviated as “P. Y. 213”), and C. I. Pigment Yellow 185(hereinafter, abbreviated as “P. Y. 185”) can be used in a yellow inkcomposition.

Aldo, commercially available C. I. Pigment Blue 15:3 (hereinafter,abbreviated as “P. B. 15:3”) can be used in a light cyan inkcomposition.

In the present invention, the pigment content in each of the cyan inkcomposition, the magenta ink composition, and the yellow ink compositionis preferably 0.1 to 15% by mass from the viewpoint of ejectionstability, storage stability, ink reliability such as clogging, and thelike.

In the present invention, each of the light cyan ink composition and thelight magenta ink composition is an ink composition having a lowerpigment concentration than that of the ink composition of a similarcolor and preferably has a pigment concentration of 2% by mass or less,more preferably 1.5 to 0.3% by mass, from the viewpoint of gradation andgraininess.

2. Components Other than Pigment

Although components other than the pigment contained in each of the inkcomposition of the present invention are not particularly limited, thecomponents below are preferably contained.

A dispersant is not particularly limited, and any dispersant which canbe used for pigment inks can be used. For example, a cationicdispersant, an anionic dispersant, a nonionic dispersant, a surfactant,and the like can be used.

Examples of the anionic dispersant include polyacrylic acid,polymethacrylic acid, acrylic acid-acrylonitrile copolymers, vinylacetate-acrylic acid ester copolymers, acrylic acid-acrylic acid alkylester copolymers, styrene-acrylic acid copolymers, styrene-methacrylicacid copolymers, styrene-acrylic acid-acrylic acid alkyl estercopolymers, styrene-methacrylic acid-acrylic acid alkyl estercopolymers, styrene-α-methylstyrene-acrylic acid copolymers,styrene-α-methylstyrene-acrylic acid-acrylic acid alkyl estercopolymers, styrene-maleic acid copolymers, vinylnaphthalene-maleic acidcopolymers, vinyl acetate-ethylene copolymers, vinyl acetate-fatty acidvinyl ethylene copolymers, vinyl acetate-maleic acid ester copolymers,vinyl acetate-crotonic acid copolymers, vinyl acetate-acrylic acidcopolymers, and the like. Examples of the nonionic dispersant includepolyvinyl pyrrolidone, polypropylene glycol, vinyl pyrrolidone-vinylacetate copolymers, and the like. Examples of the surfactant serving asthe dispersant include anionic surfactants such as sodiumdodecylbenzenesulfonate, sodium laurate, ammonium salts ofpolyoxyethylene alkyl ether sulfate, and the like; and nonionicsurfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylesters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylenealkyl phenyl ethers, polyoxyethylene alkylamines, polyoxyethylenealkylamides, and the like. In particular, styrene-(meth)acrylic acidcopolymers are preferably used from the viewpoint of enhancingdispersion stability of pigments. As described in Japanese UnexaminedPatent Application Publication No. 2007-186641, a water-insoluble vinylpolymer and the like which impart fixability and glossiness may be usedas the dispersant.

In the present invention, each of the ink compositions preferablycontains as a wetting agent at least one of polyhydric alcohols having,saccharides, and polyhydric alcohols having ethylene oxide chains. Byadding the wetting agent, an ink is prevented from being dried when usedfor ink jet recording, thereby suppressing clogging in a head of an inkjet printer.

Examples of the wetting agent include polyhydric alcohols, such asethylene glycol, diethylene glycol, triethylene glycol, polyethyleneglycol, polypropylene glycol, propylene glycol, butylene glycol,1,2,6-hexanetriol, thioglycol, hexylene glycol, glycerin,trimethylolethane, trimethylolpropane, and the like; saccharides such assugar alcohol and the like; polyhydric alcohols having ethylene oxidechains, such as ethylene glycol monoethyl ether, ethylene glycolmonobutyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, diethylene glycol monobutyl ether, triethylene glycolmonomethyl ether, triethylene glycol monoethyl ether triethylene glycolmonobutyl ether, and the like. At least one of these compounds is used.

In the present invention, each of the ink compositions preferablycontains as a penetrant at least one of pyrrolidones, alkanediols, andglycol ethers. By adding the penetrant, wettability of a recordingmedium can be enhanced to improve penetrability of ink. Examples of thepenetrant include pyrrolidones such as 2-pyrrolidone,N-methyl-2-pyrrolidone, and the like; alkanediols, such as1,2-pentanediol, 1,2-hexanediol, and the like; and glycol ethers, suchas ethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobutyl ether, triethylene glycol monobutyl ether,propylene glycol monobutyl ether, dipropylene glycol monobutyl ether,and the like. At least one of these compounds is preferably used.

In the present invention, each of the ink compositions preferablycontains as a surfactant at least one compound selected from the groupconsisting of acetylene glycols and polysiloxanes. By adding thesurfactant, wettability of a recording medium can be enhanced to improvepenetrability of ink.

In the present invention, each of the ink compositions may contain alow-boiling-point organic solvent from the viewpoint of shortening theink drying time. Examples of the low-boiling-point organic solventinclude methanol, ethanol, n-propyl alcohol, iso-propyl alcohol,n-butanol, sec-butanol, tert-butanol, iso-butanol, n-pentanol, and thelike, and at least one of these solvents is used. In particular, amonohydric alcohol is preferred.

In the present invention, each of the ink compositions preferablycontains the above-described pigment, dispersant, wetting agent,low-boiling-point organic solvent, penetrant, surfactant, and the like,and contains water as a balance. As water, pure water or ultrapurewater, such as ion exchanged water, ultrafiltered water, Milli-Q water,distilled water, or the like, is preferably used. Such water which issterilized by ultraviolet irradiation, adding hydrogen peroxide, or thelike is preferred because the occurrence of mold or bacteria isprevented over a long period of time.

In the present invention, according to demand, each of the inkcompositions may contain additives, such as a fixing agent such aswater-soluble rosin or the like, an anti-scattering agent/antisepticagent such as sodium benzoate or the like, an antioxidant/ultravioletabsorber such as allophanate or the like, a chelating agent, an oxygenabsorber, a pH adjuster, and the like, and at least one of theseadditives is used.

3. Ink Set

The ink set of the present invention includes at least the yellow inkcomposition, the magenta ink composition, the cyan ink composition, thelight cyan ink composition, the light magenta ink composition, and ablack ink composition from the viewpoint of achieving colorreproducibility in a wide range.

When the ink set of the present invention includes the black inkcomposition, a colorant thereof is not particularly limited. However, asthe colorant contained in the black ink composition, carbon black (C. I.Pigment Black 7) such as furnace black, lamp black, acetylene black,channel black, or the like, a metal compound such as copper oxide, ironoxide (C. I. Pigment Black 11), or the like, or an organic pigment suchas aniline black (C. I. Pigment Black 1) or the like can be used.However, carbon black which has relatively low specific gravity andlittle precipitates in water is preferred for ink jet. These may be usedalone or as a mixture of two. Examples of carbon black as a pigmentinclude No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7,MA8, MA100, No. 2200B, and the like which are manufactured by MitsubishiChemical Corporation; Raven 5750, 5250, 5000, 3500, 1255, and 700, andthe like which are manufactured by Columbia Chemical Co.; Regal 400R,330R, and 660R, Mogul L and 700, Monarch 800, 880, 900, 1000, 1100,1300, and 1400, and the like which are manufactured by CabotCorporation; Color Black FW1, FW2, FW2V, FW18, and FW200, Color Black5150, 5160, and 5170, Printex 35, U, V, and 140U, Special Black 6, 5,4A, and 4, and the like which are manufactured by Degussa Co. Thecomponents of the black ink composition can be controlled by the samemethod as for the above-described other ink compositions and the like.

4. Recording Method and Recording Apparatus

Although application of the ink set of the present invention is notparticularly limited, the ink set can be applied to various ink jetrecording systems. Examples of the ink jet recording systems includethermal jet-type ink jet, piezo ink jet, continuous ink jet, rollerapplication, spray application, and the like. Also, the ink set of thepresent invention can be applied to a recording apparatus and the likeusing such a recording system.

In the present invention, as a recording medium to which droplets of theink set according to the present invention are adhered, glossy paper forink jet recording is preferably used. Here, the term “glossy paper”represents plain paper in which an ink receiving layer having excellentsurface glossiness is formed by special coating. In general, there arecast glossy paper in which an ink receiving layer is formed by a castmethod to impart glossiness to a surface, and polymer-coated glossypaper in which an ink jet recording layer composed of a resin as a maincomponent is formed. As other polymer-coated glossy paper, a recordingmedium using an electron beam-curable resin can be used.

Examples

Although the present invention is described in detail below withreference to examples, the present invention is not limited to theseexamples.

1. Preparation of various ink compositions (C1, C2, C3, M1, M2, Y1, LC1,LC2, LM1, K1)

As shown in Table 1 below, each of cyan ink compositions (C1, C2, C3),magenta ink compositions (M1, M2), a yellow ink composition (Y1), lightcyan ink compositions (LC1, LC2), a light magenta ink compositions(LM1), and a black ink composition (K1) was prepared. In Table 1, theamount of each composition added is shown by % by mass. In addition, thedispersant used in Table 1 is a styrene-acrylic copolymer, and thesurfactant is BYK-348 manufactured by BYK Chemie Japan.

Further, as a quinacridone solid solution pigment contained in themagenta ink composition M2 and the light magenta ink composition LM1, asolid solution pigment containing γ-type P. V. 19 and P. R. 202 at amass ratio of 70:30 was prepared. The resulting solid solution pigmentshowed a magenta color hue, but an X-ray diffraction pattern wasdifferent from a diffraction pattern of a mixture of γ-type P. V. 19 andP. R. 202.

TABLE 1 C1 C2 C3 M1 M2 Pigment P. B. 15:3 P. B. 60 P. B. 15:6 P. V. 19Solid 4.0% 4.0% 4.0% 5.0% solution (γ-P. V. 19/P. R. 202) 5.0%Dispersant 2.4% 2.4% 2.4% 2.7% 2.7% Glycerin 9.0% 9.0% 9.0% 9.7% 11.0% 1,2-hexanediol 5.0% 5.0% 5.0% 2.5% 2.5% Triethanolamine 0.9% 0.9% 0.9%0.9% 0.9% Surfactant 0.5% 0.5% 0.5% 0.8% 0.8% Ultrapure water balancebalance balance balance balance Total 100%  100%  100%  100%  100%  Y1LC2 LC2 LM1 K1 Pigment P. B. 74 P. B. 15:3 P. B. 15:6 Solid Carbon 3.5%1.0% 1.0% solution black (γ-P. V. 2.0% 19/P. R. 202) 1.0% Dispersant2.8% 2.0% 2.0% 2.5% 1.0% Glycerin 14.0%  20.0%  20.0%  20.0%  13.0% 1,2-hexanediol 5.0% 5.0% 5.0% 2.5% 8.0% Triethanolamine 0.9% 0.9% 0.9%0.9% 0.9% Surfactant 0.5% 0.5% 0.5% 0.8% 0.3% Ultrapure water balancebalance balance balance balance Total 100%  100%  100%  100%  100% 

2. Evaluation of Ink Set 2-1 Evaluation of Color Reproduction Range

Printing was performed using an ink jet printer (“PX-5500” manufacturedby Seiko Epson Corporation). In the printer, a cyan ink cartridge (ModelNo. ICC37 manufactured by Seiko Epson Corporation), a magenta inkcartridge (Model No. ICM37 manufactured by Seiko Epson Corporation), ayellow ink cartridge (Model No. ICY37 manufactured by Seiko EpsonCorporation), and a black ink cartridge (Model No. ICBK33 manufacturedby Seiko Epson Corporation) were filled with respective ink compositionsin each of the combinations shown in Table 2, and ink sets of examplesand comparative examples were formed.

TABLE 2 Ink set Cyan Magenta Yellow Black Comparative C1 M1 Y1 K1Example 1 Comparative C2 M1 Y1 K1 Example 2 Example 1 C3 M1 Y1 K1Comparative C1 M2 Y1 K1 Example 3 Comparative C2 M2 Y1 K1 Example 4Example 2 C3 M2 Y1 K1

The thus-prepared ink cartridges were mounted on the printer, and aprinting test was conducted on photographic glossy paper (“Photopaper<Luster>” manufactured by Seiko Epson Corporation). In printing, a mixedcolor solid pattern with a duty or 85% or less was printed.

The black ink was used for finely controlling brightness.

In the specification, “duty” represents a value calculated according tothe following equation.

Duty (%)=Number of actual printing dots/(longitudinal resolution×lateralresolution)×100

(In the equation, the number of actual printing dots is the number ofactual printing dots per unit area, and longitudinal resolution andlateral resolution are each resolution per unit area. “100% duty”represents the maximum ink mass of a single color for a pixel.)

The L*a*b* color system coordinates of the resulting prints based on thecolor difference display method defined in CIE were measured using acolorimeter (Spectrolino (manufactured by Gretag Macbeth Corp.)according to JIS Z8729. FIG. 1 shows gamuts at L*=20 of Example 1 andComparative Examples 1 and 2, and FIG. 2 shows gamuts at L*=20 ofExample 2 and Comparative Examples 3 and 4. In FIG. 2, “VM” representsthe magenta ink M2.

FIG. 1 indicates that the color reproduction range in a blue region of adark portion with a L* of 20 or less can be significantly enlarged bycombining a cyan ink composition containing P. B. 15:6 or P. B. 60 as apigment with a magenta ink composition containing a quinacridone pigmentin comparison to use of a cyan ink composition containing P. B. 15:3which has been used for various purposes. In addition, FIG. 2 shows thata color with an L* value of 20 or less, an a* value of 30 or more, and ab* value of −75 or less, which has been impossible to reproduce, can berealized by combining a cyan ink composition containing P. B. 15:6 as apigment with a magenta ink composition containing a quinacridone solidsolution pigment (VM) as a pigment.

FIGS. 3, 4, and 5 show gamuts of ink sets of Example 2 and ComparativeExamples 3 and 4. In FIGS. 3 to 5, a* indicates a position between redand green colors, and negative value and positive value represent greenand red, respectively. Therefore, the more the negative a* value is, thewider the color reproduction range in a green region is. A color in thegreen region is reproduced by a cyan ink composition and a yellow inkcomposition (Y1) containing P. Y. 74 as a pigment.

In FIG. 3, the gamut of the ink set of Comparative Example 4 (ink setincluding the cyan ink composition containing P. B. 60) is shown inwhite, the gamut of the ink set of Comparative Example 3 (ink setincluding the cyan ink composition containing P. B. 15:3) is shown inblack, and a common portion of both gamuts is shown by shading.

FIG. 3 indicates that in a blue region of a dark portion, colorreproducibility of the ink set of Comparative Example 3 using P. B. 15:3as a pigment is inferior to the ink set using P. B. 60 as a pigment(Comparative Example 4) (refer to FIGS. 1 and 2), while in a greenregion, the ink set of Comparative Example 3 shows good colorreproducibility. For example, in a region with L* of 10 to 40, a blackportion is wide within a region of negative a* values. Namely, it isshown that the ink set (Comparative Example 3) using P. B. 15:3 haswider color reproducibility in a green region as compared with the inkset (Comparative Example 4) using P. B. 60.

On the other hand, in FIG. 4, the gamut of the ink set of Example 2 (inkset including the cyan ink composition containing P. B. 15:6) is shownin white, the gamut of the ink set of Comparative Example 3 (ink setincluding the cyan ink composition containing P. B. 15:3) is shown inblack, and a common portion of both gamuts is shown by shading.

FIG. 4 indicates that in a blue region of a dark portion, the ink set ofExample 2 using P. B. 15:6 as a pigment has excellent colorreproducibility and, in a green region, the ink set of Example 2 haswide color reproducibility equivalent to the ink set of ComparativeExample 3 using P. B. 15:3 as a pigment.

In FIG. 5, the gamut of the ink set of Example 2 (ink set including thecyan ink composition containing P. B. 15:6) is shown in white, the gamutof the ink set of Comparative Example 4 (ink set including the cyan inkcomposition containing P. B. 60) is shown in black, and a common portionof both gamuts is shown by shading.

FIG. 5 indicates that in both the blue region and the green region, theink set using P. B. 15:6 as a pigment has wider color reproducibilitythan that of the ink set using P. B. 60 as a pigment.

2-2 Evaluation of Graininess in High-Brightness Region

Next, printing was performed using an ink jet printer (“PX-5500”manufactured by Seiko Epson Corporation). In the printer, a cyan inkcartridge (Model No. ICC37 manufactured by Seiko Epson Corporation), amagenta ink cartridge (Model No. ICM37 manufactured by Seiko EpsonCorporation), a yellow ink cartridge (Model No. ICY37 manufactured bySeiko Epson Corporation), a black ink cartridge (Model No. ICBK33manufactured by Seiko Epson Corporation), a light cyan ink cartridge(Model No. ICLC37 manufactured by Seiko Epson Corporation), and a lightmagenta ink cartridge (Model No. ICLM37 manufactured by Seiko EpsonCorporation) were filled with respective ink compositions in each of thecombinations shown in Table 3, and ink sets of an example and acomparative example were formed.

TABLE 3 Ink set Light Light Cyan Magenta Yellow cyan magenta BlackComparative C3 M1 Y1 LC2 LM1 K1 Example 5 Example 3 C3 M1 Y1 LC1 LM1 K1

The thus-prepared ink cartridges were mounted on the printer, and agradation patch including 14 evaluation images with L* values of 50 to95 of green and cyan colors was printed on photographic glossy paper(“Photopaper <Luster>” manufactured by Seiko Epson Corporation). Theresulting print was taken in as electron data by a scanner (“GT-X770”manufactured by Seiko Epson Corporation), and graininess index valueswere calculated with a dedicated software. In addition, the scanresolution was 1200 dpi, and an analysis region was 256×256 pixels.

FIG. 6 is a chart showing the results of evaluation of graininess of 14types of evaluation images in the green region. Also, FIG. 7 is a chartshowing the results of evaluation of graininess of 14 types ofevaluation images in the cyan region.

The graininess was evaluated using the dedicated software on the basisof graininess index value GF shown by equation 1 below. In the equation,u is a spatial frequency, WS(u) is a Wiener spectrum of an image, VTF(u)is visual sensitivity characteristic with respect to the spatialfrequency, and L is an observation distance (300 mm). In addition,(L*+16/116)^(0.8) is a factor for adjusting the index value to the humanvisual characteristics.

GF=(L*+16/116)^(0.8) ∫WS(u)^(0.5) ·VTF(u)du  Equation 1

wherein

VTF(u)=5.05 exp(−0.318πLu/180)[1−exp(−0.1πLu/180)]

Here, the meaning of equation 1 is briefly described. WS(u) isconsidered to indicate the periodicity of an image. For example,considering an image in which a large filled circle pattern isrepeatedly printed, large peaks appear, in a WS(u) spectrum of theimage, at spatial frequency u1 corresponding to the diameter of thefilled circles and spatial frequency u2 corresponding to the repetitionperiod of the filled circles. Conversely, when peaks appear at spatialfrequencies u1 and u2 in a WS(u) spectrum, it is considered that theimage includes two periodic structures corresponding to the respectivespatial frequencies.

In addition, it has been found that the sensitivity of the human eyedepends on the spatial frequency, and there is spatial frequency up atwhich the sensitivity is highest. Namely, the human eye has thecharacteristic that the sensitivity increases as the spatial frequencycomes closer to the spatial frequency up, and the sensitivity decreasesas the spatial frequency comes away from the spatial frequency up.Therefore, in an image including repeated filled circles, the filledcircles become more noticeable as one of the spatial frequency u1corresponding to the diameter of the filled circles and the spatialfrequency u2 corresponding to the repetition period of the filledcircles comes closer to the spatial frequency up. Conversely, the filledcircles become less noticeable as the spatial frequency u1 and thespatial frequency u2 come away from the spatial frequency up. Also, theblackness of the filled circles influences noticeability. That is, it issaid that if filled circles are the same size, a filled circuit of darkcolor formed with a dark ink such as K ink is more noticeable than afilled circle of light color formed with a light ink such as LK ink orLLK ink. The influence of blackness of filled circles is reflected asthe intensity of WS(u). The WS(u) is calculated by two-dimensional fastFourier transform (FFT) of a L* component image formed by colorconversion of scan image data and then converting to a one-dimensionalpolar coordinate system.

The evaluation equation according to equation 1 quantifies graininess onthe basis of the above-described human eye characteristics. Namely,noticeability of dots (graininess of image) is quantified as graininessindex value GF by human-eye-weighting WS(u) showing periodicity of animage and integrating WS(u) with respect to spatial frequency (referencedocument: Makoto Fujino, The Imaging Society of Japan “Japan Hardcopy'99” P. 291-294).

FIGS. 6 and 7 indicate that as the L* value increases, the graininessindex increases, and thus graininess deteriorates. It is found thatparticularly in a high-brightness region with an L* of 80 or more,deterioration of graininess can be significantly suppressed using P. B.15:3.

As described above, the ink set according to the present invention canreproduce a color in a dark portion blue region having an L* value of 20or less, an a* value of 30 or more, and a b* value of −75 or lessaccording to CIE standards, which has so far been impossible toreproduce. Also, the ink set has excellent color reproducibility in agreen region and can form a high-quality image with excellent graininesseven in a high-brightness cyan region and green region.

1. An ink set comprising: a cyan ink composition containing C. I.Pigment Blue 15:6 as a pigment; a magenta ink composition containing aquinacridone pigment selected from the group consisting of C. I. PigmentViolet 19, C. I. Pigment Red 122, C. I. Pigment Red 202, and C. I.Pigment Red 209 or a quinacridone solid solution pigment composed of atleast two selected from the group; a yellow ink composition containing apigment selected from the group consisting of C. I. Pigment Yellow 74,C. I. Pigment Yellow 213, and C. I. Pigment Yellow 185; a light magentaink composition containing a quinacridone pigment selected from thegroup consisting of C. I. Pigment Violet 19, C. I. Pigment Red 122, C.I. Pigment Red 202, and C. I. Pigment Red 209 or a quinacridone solidsolution pigment composed of at least two selected from the group at apigment concentration lower than that of the magenta ink composition;and a light cyan ink composition containing C. I. Pigment Blue 15:3 as apigment at a pigment concentration lower than that of the cyan inkcomposition.
 2. The ink set according to claim 1, wherein the pigmentcontained in at least one of the magenta ink composition and the lightmagenta ink composition is a quinacridone solid solution pigmentcomposed of at least two selected from the group consisting of C. I.Pigment Violet 19, C. I. Pigment Red 122, C. I. Pigment Red 202, and C.I. Pigment Red
 209. 3. The ink set according to claim 2, wherein thepigment contained in at least one of the magenta ink composition and thelight magenta ink composition is a quinacridone solid solution pigmentcomposed of C. I. Pigment Violet 19 and C. I. Pigment Red
 202. 4. Theink set according to claim 3, wherein in the quinacridone solid solutionpigment, the mass of C. I. Pigment Violet 19 is larger than the mass ofC. I. Pigment Red
 202. 5. The ink set according to claim 3, wherein inthe quinacridone solid solution pigment, the mass ratio of C. I. PigmentViolet 19/C. I. Pigment Red 202 is 70/30 to 50/50.
 6. The ink setaccording to claim 1, wherein C. I. Pigment Violet 19 contained in thequinacridone solid solution pigment is γ-type.
 7. The ink set accordingto claim 1, wherein the pigment concentration in each of the lightmagenta ink composition and the light cyan ink composition is 2% by massor less.
 8. The ink set according to claim 1 comprising the cyan inkcomposition, the magenta ink composition, the yellow ink composition,the light magenta ink composition, the light cyan ink composition, and ablack ink composition.
 9. A recording apparatus comprising the ink setaccording to claim
 1. 10. A recording method using the ink set accordingto claim 1.